1. Field of the Invention
This invention relates to methods of forming articles consisting of particles of sintered or cast tungsten carbide disposed in a tungsten, carbon steel alloy matrix and to composite structures formed by this method.
2. Prior Art
Composites consisting of sintered or cast metallic carbide particles or chunks supported in a matrix of a more resilient metal are often employed in high wear applications. The wear resistance of the sintered particles is complemented by the toughness of the matrix to form a material that is more abrasion resistant than the matrix material and can withstand impact loads better than the sintered carbide.
Articles formed from these composite materials are used in applications where they are subjected to regular contact with hard, abrasive materials as conventional materials either wear too quickly or lack the impact resistance to withstand use over a long period. For example, they may be employed in ore treatment plants as chutes, or as facings on rock drills. They may also be employed in security applications such as for locks and safes because of their resistance to penetration by drills and like tools.
The failure mode of the composites in high abrasion typically involves the erosion of the matrix portion of a surface until a substantial portion of a sintered particle is exposed, and then the tearing away of that particle from the matrix. Efforts to improve the composite to minimize this failure mode have been directed toward use of harder matrix materials to minimize their erosion. But this usually increases the brittleness of the matrix making it easier for a particle to break away by cracking at the matrix-particle interface.
Previous efforts to form composite materials consisting of tungsten carbide particles in a softer metal matrix have been directed toward avoidance of any dissolving of the tungsten carbide or deterioration of the sintered material as a result of the heat of the molten matrix. In most applications matrixing alloys have been used with melting points substantially below about 2650.degree. F., the temperatures at which components of the tungsten carbide begin to diffuse into the alloys. Typically, copper based alloys have been employed for the matrix because of their low melting temperatures in the range of 1900.degree. F. to 2100.degree. F. In applications where a harder matrixing material is required, using metals with melting temperatures close to the temperature at which the metallic carbide dissolves, attempts have been made to very carefully control the temperature at which the composite is formed to minimize the amount of sintered material dissolved in the matrix. For example, U.S. Pat. Nos. 3,175,260 and 3,149,411 disclose methods wherein the steel matrix is heated to a temperature only sufficient to allow it to be poured over and infiltrate the tungsten carbide particles disposed in a mold. The particles are preheated to this infiltration temperature and the composite is maintained at this temperature for a sufficient time after pouring to insure thorough infiltration of the particle mass by the matrix material.